The next generation of military and civilian communications products will incorporate the ability to dynamically adjust their use of spectrum based on measurements of the installed environment. Such “cognitive” radios must be capable of operating on a wide range of different radio frequencies. At the same time, the ubiquitous nature of wireless communications is producing an environment where a single user desires to receive information from multiple independent sources, which, once again, may be operating in completely different spectral regions.
The US Department of Defense has recognized that it is desirable to have basic radio that can operate on multiple channels spaced over many separate frequency bands. The DoD has invested billions of dollars in the Joint Tactical Radio System (JTRS) to accomplish this goal. The JTRS radios are intended to operate over the range of 2 MHz (2,000,000 Hz) to 2 GHz (2,000,000,000 Hz). Depending on options, the JTRS radios may contain one, two, four, six, or more receive and transmit channels. Typical JTRS radios, such as those known as the Cluster 1 radios, occupy a volume of some 28,000 cubic centimeters (cm3) and consume 100 watts of power. JTRS radios contain receiver hardware, transmitter hardware, and extensive software for waveform processing and link and network layer control. Prices for an individual JTRS radio may exceed $100,000.
The key to the JTRS program is the processing of the received waveforms by software controlled digital techniques. In particular, the JTRS architecture relies on conversion of the analog received signals to digital form at the soonest possible point in the radio architecture, followed by digital filtering and down conversion functions in either high-speed digital hardware or powerful digital signal processor ships. This requires high sample rate analog-to-digital converters, high-speed FPGAs, and powerful DSPs capable of billions of operations per second (GFLOPs/sec). In addition, the JTRS software architecture requires a powerful general purpose processor with a significant amount of memory. The net result is that multichannel JTRS units are sizable, relatively heavy, and power-hungry.